Dielectric relaxation in the PbFe1/2Nb1/2O3 ceramics

Obtaining, structure, microstructure and dielectric characteristics of ceramics and thin films of ferro-piezoelectric materials based on the PZT system

“…The latter is associated with an increase in the electrical conductivity of materials and, as a consequence, an increase in the contribution to the recorded dielectric response of mechanisms interlayer polarization effects. 20 In the range f > 10 6 Hz, the effect of increasing " 0 /" 0 is absent in the studied temperature range.…”

Phase states, microstructure and dielectric characteristics of solid solutions (1 – x)NaNbO3 – xCa2Nb2O7 and (1 – x)NaNbO3 – xSr2Nb2O7

“…This type of relaxation suggests the contribution of through conductivity to the dielectric response of the studied samples. Moreover, this contribution can be significant, as previous studies show [24]. A theoretical description of the temperature-frequency dependences of the real and imaginary parts ε*/ε 0 in the studied frequency range was carried out in the framework of the linear dielectric model with various relaxation time distribution functions.…”

“…The approximation results are presented concurrently on Figure 12 Maxwell-Wagner polarization and the corresponding relaxation can be the basis of the physical model describing the observed phenomenon. This type of polarization often called "interlayer", is manifested, in particular, in an electrically inhomogeneous matrix medium consisting of cells of approximately isodiametric ceramic grains (crystallites), which are surrounded by thin layers with high [25] or low [24,26] conductivity and ε* different from that of the grains. Observed in this work large variety of grain types, often having different shape and characteristics, leads to the appearance of interlayer polarization and dielectric relaxation in the studied objects.…”

Progress of Relaxor Multiferroic Materials

“…The value of the maximum dielectric constant  m could reach above 10,000. The relation between the T m and frequency could be described by V-F function 类似地, 还存在纳米尺度的短程磁有序(NMR) 材料, 其磁性介于长程磁有序材料(铁磁体、亚铁磁 体和反铁磁体)和顺磁材料之间。科学家把短程磁有 序为主的材料称为弛豫铁磁体 [18][19] 。通常采用自旋 玻璃态解释弛豫铁磁体的磁性。在弛豫铁磁体中, 电子的自旋不再统一排列, 而是随机取向, 这种随 机取向不再随时间的改变而变化, 即存在空间坐标 上的"无序"和时间坐标上的"有序"(图 2)。与之 相应, 材料表现出一些新奇的物理效应。 比如, 其交 流磁化率与温度曲线在玻璃态转变温度 T g 附近表 现出异常峰, 并且该异常峰与频率明显相关, 可以 通过 V-F 方程来描述; 在很低的外加直流磁场作用 下, 该异常峰就可被抹平。再比如, 在带场冷却 FC 和零场冷却 ZFC 两种测量条件下, 磁化率在 T g 以下 表现出明显的背离。 [12] 。自由能表示如下: [20][21][22] 。而对于 B 晶格位铁磁活性离子 (Fe 3+ )与铁电活性离子比例为 1 : 1 的 PbFe 1/2 Nb 1/2 O 3 和 PbFe 1/2 Ta 1/2 O 3 , 铁电序基本以长程有序为主, 铁 电结构为四方(空间群 P4mm)相, 后者居里点低于 室温 [23][24][25][26][27] [31] Fig. 3 Schematic representation of Fe 3+ spins arrangement for PbFe 2/3 W 1/3 O 3 , The frustrated Fe 3+ spins appear in AFM sublattices [31] 2007 年, Levstik 研究组 [32] 发现, 在 Increase of the magnetic field H leads to decrease in P r .…”

“…P r is nearly zero when H reaches 0.5 T. This effect disappears after magnetic field being removed. Correspondingly, the anomaly peak of the imaginary part for dielectric constant shifts to the low frequency side with H increasing, which reveals the increase of the relaxation time 的, 通过 Landau-Devonshire 理论, 确定 PNR 的尺寸 为 7~11 nm。 在 BiFeO 3 中引入 BaTiO 3 , 可以形成 BiFeO 3 -BaTiO 3 固溶体系。 研究发现, 随着 BiFeO 3 含量增加, 该体系存在铁电-弛豫转变, 可以表现出弛豫铁电 态和亚铁磁性的共存 [46][47][48][49] 。 该体系三方-准立方相界 附近的 0.67BiFeO 3 -0.33BaTiO 3 以单晶形式存在时, 则表现出更加丰富的磁电性质, 通过中子漫散射实 验, 日本研究者证实了该单晶在 600 K 附近存在 8 nm 左右的 PNR(图 6) [50] 。随着温度上升, PNR 变小, 在 800 K 附近 PNR 消失。此外, 该单晶表现出超顺磁 [31] Ferroelectric relaxor T m = 210 K @0.1 MHz T f = 164 K Anti-ferromagnetic T N = 350 K Magnetic glass state T g = 10 K PbFe 0.5 Nb 0.5 O 3 ceramics [23,29] Ferroelectric T m =373 K Anti-ferromagnetic T N = 153 K Magnetic glass state T g = 10.6 K PbFe 0.5 Ta 0.5 O 3 ceramics [27,30] Ferroelectric T m = 259 K Anti-ferromagnetic T N = 153 K Magnetic glass state T g < 10 K 0.8PbFe 1/2 Nb 1/2 O 3 -0.2PbMg 1/2 W 1/2 O 3 ceramics [32] Ferroelectric relaxor T m = 280 K @0.1 MHz T f = 245 K Magnetic glass state T g = 25K Pb(Fe 0.66 W 0.33 ) 0.8 Ti 0.2 O 3 thin films [33] Ferroelectric relaxor T m = 350 K @ 10 kHz T f = 238 K Ferrimagnetic Pb(Fe 0.66 W 0.33 ) 0.2 (Zr 0.53 Ti 0.47 ) 0.8 O 3 thin film [36] Ferroelectric relaxor T m < 600 K @ 1 MHz Ferrimagnetic Pb(Zr 0.53 Ti 0.47 ) 0.60 (Fe 0.5 Ta 0 . 5 ) 0.4 O 3 thin films [37] Ferroelectric relaxor T m = 390 K @1 MHz T f = 305 K Ferrimagnetic 图 5 基于弛豫多铁性材料的多态存储器 Fig.…”